Transcript Chap. 17 Conceptual Modules Fishbane

ConcepTest 16.1
Which is the largest unit: one
Celsius degree, one Kelvin
degree, or one Fahrenheit
degree?
Degrees
1) one Celsius degree
2) one Kelvin degree
3) one Fahrenheit degree
4) both one Celsius degree and
one Kelvin degree
5) both one Fahrenheit degree
and one Celsius degree
ConcepTest 16.1
Which is the largest unit: one
Celsius degree, one Kelvin
degree, or one Fahrenheit
degree?
Degrees
1) one Celsius degree
2) one Kelvin degree
3) one Fahrenheit degree
4) both one Celsius degree and
one Kelvin degree
5) both one Fahrenheit degree
and one Celsius degree
The Celsius degree and the Kelvin degree are the same size. The
scales only differ by an offset, not by the size of the degree unit. For
Fahrenheit, there are 180 degrees between boiling and freezing
(212°F–32°F). For Celsius, there are 100 degrees between the same
points, so the Celsius (and Kelvin) degrees must be larger.
ConcepTest 16.2
Freezing Cold
It turns out that – 40°C is the same
temperature as – 40°F. Is there a
temperature at which the Kelvin and
Celsius scales agree?
1) yes, at 0 °C
2) yes, at -273 °C
3) yes, at 0 K
4) no
ConcepTest 16.2
Freezing Cold
It turns out that – 40°C is the same
temperature as – 40°F. Is there a
temperature at which the Kelvin and
Celsius scales agree?
1) yes, at 0 °C
2) yes, at -273 °C
3) yes, at 0 K
4) no
The Celsius and Kelvin scales differ only by an offset, which is 273
degrees. Therefore, a temperature on one scale can never match the
same numerical value on the other scale. The reason that such
agreement is possible for Celsius and Fahrenheit is the fact that the
actual degree units have different sizes (recall the previous question).
ConcepTest 16.3
Thermometers
1) the mercury contracts before the
You may notice that if a
glass contracts
mercury-in-glass thermometer 2) the glass contracts before the
is inserted into a hot liquid, the
mercury contracts
mercury column first drops,
3) the mercury contracts before the
glass expands
and then later starts to rise (as
4) the glass expands before the
you expect). How do you
mercury expands
explain this drop?
5) the mercury expands before the
glass contracts
ConcepTest 16.3
Thermometers
1) the mercury contracts before the
You may notice that if a
glass contracts
mercury-in-glass thermometer 2) the glass contracts before the
is inserted into a hot liquid, the
mercury contracts
mercury column first drops,
3) the mercury contracts before the
glass expands
and then later starts to rise (as
4) the glass expands before the
you expect). How do you
mercury expands
explain this drop?
5) the mercury expands before the
glass contracts
The hot liquid touches the glass first, so initially the glass
expands slightly. This increases the volume inside the glass,
and so the mercury level drops slightly. Once the mercury
heats up, it begins to expand and then the characteristic rise
in the mercury column follows, indicating the increase in
temperature that you expected to measure.
Follow-up: Is it possible to have the mercury first rise and later drop?
ConcepTest 16.4
Glasses
1) run hot water over them both
Two drinking glasses are
stuck, one inside the other.
How would you get them
unstuck?
2) put hot water in the inner one
3) run hot water over the outer one
4) run cold water over them both
5) break the glasses
ConcepTest 16.4
Glasses
1) run hot water over them both
Two drinking glasses are
stuck, one inside the other.
How would you get them
unstuck?
2) put hot water in the inner one
3) run hot water over the outer one
4) run cold water over them both
5) break the glasses
Running hot water only over the outer glass will
allow the outer one to expand, while the inner glass
remains relatively unchanged. This should loosen
the outer glass and free it.
ConcepTest 16.5a
Steel Expansion I
A steel tape measure is
marked such that it gives
accurate length measurements 1) measured lengths will be too small
at room temperature. If the
2) measured lengths will still be accurate
tape measure is used outside
on a very hot day, how will its 3) measured lengths will be too big
length measurements be
affected?
ConcepTest 16.5a
Steel Expansion I
A steel tape measure is
marked such that it gives
accurate length measurements 1) measured lengths will be too small
at room temperature. If the
2) measured lengths will still be accurate
tape measure is used outside
on a very hot day, how will its 3) measured lengths will be too big
length measurements be
affected?
The tape measure will expand, so its markings will spread out
farther than the correct amount. When it is laid down next to an
object of fixed length, you will read too few markings for that given
length, so the measured length will be too small.
ConcepTest 16.5b
Steel Expansion II
Metals such as brass expand when
heated. The thin brass plate in the
movie has a circular hole in its
center. When the plate is heated,
what will happen to the hole?
1) gets larger
2) gets smaller
3) stays the same
4) vanishes
ConcepTest 16.5b
Steel Expansion II
Metals such as brass expand when
heated. The thin brass plate in the
movie has a circular hole in its
center. When the plate is heated,
what will happen to the hole?
1) gets larger
2) gets smaller
3) stays the same
4) vanishes
Imagine drawing a circle on the
plate. This circle will expand
outward along with the rest of the
plate. Now replace the circle with
the hole, and you can see that the
hole will expand outward as well.
Note that the material does NOT
“expand inward” to fill the hole!!
expansion
ConcepTest 16.6a
Steel Ring I
A steel ring stands on edge with a rod of
some material inside. As this system is
heated, for which of the following rod
materials will the rod eventually touch
the top of the ring?
1) aluminum
2) steel
3) glass
4) aluminum and steel
5) all three
Quartz
Glass Steel Al



Hg
Air

Coefficient of volume expansion b (1/°C )
ConcepTest 16.6a
Steel Ring I
A steel ring stands on edge with a rod of
some material inside. As this system is
heated, for which of the following rod
materials will the rod eventually touch
the top of the ring?
1) aluminum
2) steel
3) glass
4) aluminum and steel
5) all three
Quartz
Glass Steel Al



Hg
Air

Coefficient of volume expansion b (1/°C )
Aluminum is the only material that has a larger b value than
the steel ring, so that means that the aluminum rod will
expand more than steel ring. Thus, only in that case does
the rod have a chance of reaching the top of the steel ring.
ConcepTest 16.6b
Steel Ring II
You want to take apart a couple of
1) heat the thing up
aluminum parts held together by
2) cool the thing down
steel screws, but the screws are
3) blow the thing up
stuck. What should you do?
Quartz
Glass Steel Al



Hg
Air

Coefficient of volume expansion b (1/°C )
ConcepTest 16.6b
Steel Ring II
You want to take apart a couple of
1) heat the thing up
aluminum parts held together by
2) cool the thing down
steel screws, but the screws are
3) blow the thing up
stuck. What should you do?
Quartz
Glass Steel Al



Hg
Air

Coefficient of volume expansion b (1/°C )
Since aluminum has a larger b value, that means aluminum
expands more than steel. Thus, by heating the part, the
aluminum holes will expand faster than the steel screws and the
screws will come loose.
ConcepTest 16.8a
Two objects are made of
the same material, but have
different masses and
temperatures. If the
objects are brought into
thermal contact, which one
will have the greater
temperature change?
Thermal Contact I
1) the one with the higher initial temperature
2) the one with the lower initial temperature
3) the one with the greater mass
4) the one with the smaller mass
5) the one with the higher specific heat
ConcepTest 16.8a
Two objects are made of
the same material, but have
different masses and
temperatures. If the
objects are brought into
thermal contact, which one
will have the greater
temperature change?
Thermal Contact I
1) the one with the higher initial temperature
2) the one with the lower initial temperature
3) the one with the greater mass
4) the one with the smaller mass
5) the one with the higher specific heat
Since the objects are made of the same material, the only difference
between them is their mass. Clearly, the object with less mass will
change temperature more easily since not much material is there
(compared to the more massive object).
ConcepTest 16.8b
Two different objects
receive the same amount
of heat. Which of the
following choices is NOT
a reason why the objects
may have different
temperature changes?
Thermal Contact II
1) they have different initial temperatures
2) they have different masses
3) they have different specific heats
ConcepTest 16.8b
Two different objects
receive the same amount
of heat. Which of the
following choices is NOT
a reason why the objects
may have different
temperature changes?
Thermal Contact II
1) they have different initial temperatures
2) they have different masses
3) they have different specific heats
Since Q = m c DT and the objects received the same amount of
heat, the only other factors are the masses and the specific heats.
While the initial temperature is certainly relevant for finding the
final temperature, it does not have any effect on the temperature
change DT.
ConcepTest 16.9
Two Liquids
Two equal-mass liquids, initially at the
same temperature, are heated for the same
1) the cooler one
time over the same stove. You measure
2) the hotter one
the temperatures and find that one liquid
has a higher temperature than the other.
Which liquid has a higher specific heat?
3) both the same
ConcepTest 16.9
Two Liquids
Two equal-mass liquids, initially at the
same temperature, are heated for the same
1) the cooler one
time over the same stove. You measure
2) the hotter one
the temperatures and find that one liquid
has a higher temperature than the other.
3) both the same
Which liquid has a higher specific heat?
Both liquids had the same increase in internal energy,
because the same heat was added.
But the cooler liquid
had a lower temperature change.
Since Q = mcDT, if Q and m are both the same and DT is
smaller, then c (specific heat) must be bigger.
ConcepTest 16.10a
The specific heat of concrete is
greater than that of soil. A baseball
field (with real soil) and the
surrounding parking lot are warmed
up during a sunny day. Which would
you expect to cool off faster in the
evening when the sun goes down?
Night on the Field
1) the concrete parking lot
2) the baseball field
3) both cool off equally fast
ConcepTest 16.10a
The specific heat of concrete is
greater than that of soil. A baseball
field (with real soil) and the
surrounding parking lot are warmed
up during a sunny day. Which would
you expect to cool off faster in the
evening when the sun goes down?
Night on the Field
1) the concrete parking lot
2) the baseball field
3) both cool off equally fast
The baseball field, with the lower specific heat, will change
temperature more readily, so it will cool off faster. The high specific
heat of concrete allows it to “retain heat” better and so it will not cool
off so quickly – it has a higher “thermal inertia.”
ConcepTest 16.10b
Night on the Beach
Water has a higher specific
(1) from the ocean to the beach
heat than sand. Therefore,
(2) from the beach to the ocean
on the beach at night,
breezes would blow:
(3) either way, makes no difference
ConcepTest 16.10b
Water has a higher specific
(1) from the ocean to the beach
heat than sand. Therefore,
(2) from the beach to the ocean
on the beach at night,
breezes would blow:

Night on the Beach
(3) either way, makes no difference
Daytime
 sun heats both the beach and the water
» beach heats up faster
» warmer air above beach rises
» cooler air from ocean moves in underneath
» breeze blows ocean  land

csand < cwater
Nighttime
 sun has gone to sleep
» beach cools down faster
» warmer air is now above the ocean
» cooler air from beach moves out to the ocean
» breeze blows land  ocean
ConcepTest 16.11
Calorimetry
(1) 0 oC
1 kg of water at 100 oC is poured into a
(2) 20 oC
bucket that contains 4 kg of water at 0
(3) 50 oC
oC.
(4) 80 oC
Find the equilibrium temperature
(neglect the influence of the bucket).
(5) 100 oC
ConcepTest 16.11
Calorimetry
(1) 0 oC
1 kg of water at 100 oC is poured into a
(2) 20 oC
bucket that contains 4 kg of water at 0
(3) 50 oC
oC.
(4) 80 oC
Find the equilibrium temperature
(neglect the influence of the bucket).
Since the cold water mass is greater, it will
have a smaller temperature change!
(5) 100 oC
Q1 = Q2
The masses of cold/hot have a ratio of 4:1,
m1cDT1 = m2cDT2
so the temperature change must have a
DT1 / DT2 = m2 / m1
ratio of 1:4 (cold/hot).
ConcepTest 17.1a
Nitrogen and Oxygen I
Which has more molecules – a
mole of nitrogen (N2) gas or a
mole of oxygen (O2) gas?
1) oxygen
2) nitrogen
3) both the same
ConcepTest 17.1a
Nitrogen and Oxygen I
Which has more molecules – a
mole of nitrogen (N2) gas or a
mole of oxygen (O2) gas?
1) oxygen
2) nitrogen
3) both the same
A mole is defined as a quantity of gas molecules equal to
Avogadro’s number (6.02  1023). This value is independent of the
type of gas.
ConcepTest 17.1b
Nitrogen and Oxygen II
Which weighs more – a mole
1) oxygen
of nitrogen (N2) gas or a mole
2) nitrogen
of oxygen (O2) gas?
3) both the same
ConcepTest 17.1b
Nitrogen and Oxygen II
Which weighs more – a mole
1) oxygen
of nitrogen (N2) gas or a mole
2) nitrogen
of oxygen (O2) gas?
3) both the same
The oxygen molecules have a molecular mass of 32, while the
nitrogen molecules have a molecular mass of 28.
Follow-up: Which one will take up more space?
ConcepTest 17.2a
Ideal Gas Law I
Two identical cylinders at the same
1) cylinder A
temperature contain the same gas. If
2) cylinder B
A contains three times as much gas
as B, which cylinder has the higher
pressure?
3) both the same
4) it depends on temp. T
ConcepTest 17.2a
Ideal Gas Law I
Two identical cylinders at the same
1) cylinder A
temperature contain the same gas. If
2) cylinder B
A contains three times as much gas
as B, which cylinder has the higher
3) both the same
4) it depends on temp. T
pressure?
Ideal gas law: PV = nRT
Solve for pressure: P = nRT / V
For constant V and T, the one with more
gas (the larger value of n)
higher pressure P.
has the
ConcepTest 17.2b
Ideal Gas Law II
Two identical cylinders at the same
1) cylinder A
pressure contain the same gas. If A
2) cylinder B
contains three times as much gas as
3) both the same
B, which cylinder has the higher
temperature?
4) it depends on the
pressure P
ConcepTest 17.2b
Ideal Gas Law II
Two identical cylinders at the same
1) cylinder A
pressure contain the same gas. If A
2) cylinder B
contains three times as much gas as
3) both the same
B, which cylinder has the higher
temperature?
4) it depends on the
pressure P
Ideal gas law: PV = nRT
Solve for temperature: T = PV / nR
For constant V and P, the one with less gas
(the smaller value of n) has the higher
temperature T.
ConcepTest 17.2c
Two identical cylinders at the same
temperature contain the same gas.
If B has twice the volume and half
Ideal Gas Law III
1) PB = 1/2 PA
2) PB = 2 PA
the number of moles as A, how does
3) PB = 1/4 PA
the pressure in B compare with the
4) PB = 4 PA
pressure in A?
5) PB = PA
ConcepTest 17.2c
Two identical cylinders at the same
temperature contain the same gas.
If B has twice the volume and half
Ideal Gas Law III
1) PB = 1/2 PA
2) PB = 2 PA
the number of moles as A, how does
3) PB = 1/4 PA
the pressure in B compare with the
4) PB = 4 PA
pressure in A?
5) PB = PA
Ideal gas law: PV = nRT
Since B has a factor of twice the volume, it has a factor of
two less the pressure. But B also has half the amount of
gas, so that is another factor of two reduction in pressure.
Thus, B must have only 1/4 the pressure of A.
ConcepTest 17.3
A plastic soda bottle is empty
and sits out in the sun,
heating the air inside. Now
you put the cap on tightly and
put the bottle in the fridge.
What happens to the bottle as
it cools?
Soda Bottle
1) it expands and may burst
2) it does not change
3) it contracts and the sides collapse
inward
4) it is too dark in the fridge to tell
ConcepTest 17.3
A plastic soda bottle is empty
and sits out in the sun,
heating the air inside. Now
you put the cap on tightly and
put the bottle in the fridge.
What happens to the bottle as
it cools?
Soda Bottle
1) it expands and may burst
2) it does not change
3) it contracts and the sides collapse
inward
4) it is too dark in the fridge to tell
The air inside the bottle is warm, due to heating by the
sun. When the bottle is in the fridge, the air cools. As the
temperature drops, the pressure in the bottle also drops.
Eventually, the pressure inside is sufficiently lower than
the pressure outside (atmosphere) to begin to collapse
the bottle.
ConcepTest 17.4
Balloon in Freezer
1) it increases
What happens to the volume
of a balloon if you put it in the
freezer?
2) it does not change
3) it decreases
ConcepTest 17.4
Balloon in Freezer
1) it increases
What happens to the volume
of a balloon if you put it in the
freezer?
2) it does not change
3) it decreases
According to the Ideal Gas Law, when the temperature is
reduced at constant pressure, the volume is reduced as well.
The volume of the balloon therefore decreases.
PV = nRT
Follow-up: What happens to the volume
when the balloon rises in the air?
ConcepTest 17.5
If you add some heat to a substance,
is it possible for the temperature of
the substance to remain unchanged?
Adding Heat
1) yes
2) no
ConcepTest 17.5
If you add some heat to a substance,
is it possible for the temperature of
the substance to remain unchanged?
Adding Heat
1) yes
2) no
Yes, it is indeed possible for the temperature to stay the same. This is
precisely what occurs during a phase change – the added heat goes
into changing the state of the substance (from solid to liquid or from
liquid to gas) and does not go into changing the temperature! Once
the phase change has been accomplished, then the temperature of the
substance will rise with more added heat.
Follow-up: Does that depend on the substance?
ConcepTest 17.6
Will potatoes cook faster if the
water is boiling faster?
Hot Potato
1) yes
2) no
ConcepTest 17.6
Will potatoes cook faster if the
water is boiling faster?
Hot Potato
1) yes
2) no
The water boils at 100 °C and remains at that temperature until all
of the water has been changed into steam. Only then will the
steam increase in temperature. Since the water stays at the same
temperature, regardless of how fast it is boiling, the potatoes will
not cook any faster.
Follow-up: How can you cook the potatoes faster?
ConcepTest 17.7
You put 1 kg of ice at 0oC
together with 1 kg of water at
50oC. What is the final
temperature?
LF = 80 cal/g
cwater = 1 cal/g oC
Water and Ice
1) 0oC
2) between 0oC and 50oC
3) 50oC
4) greater than 50oC
ConcepTest 17.7
You put 1 kg of ice at 0oC
together with 1 kg of water at
50oC. What is the final
temperature?
LF = 80 cal/g
cwater = 1 cal/g oC
Water and Ice
1) 0oC
2) between 0oC and 50oC
3) 50oC
4) greater than 50oC
How much heat is needed to melt the ice?
Q = m Lf = (1000g)  (80 cal/g) = 80,000 cal
How much heat can the water deliver by cooling from 50oC to 0oC?
Q = cwater m DT = (1 cal/g oC)  (1000g)  (50oC) = 50,000 cal
Thus, there is not enough heat available to melt all the ice!!
Follow-up: How much more water at 50oC would you need?
ConcepTest 17.8
You put 1 kg of ice at 0oC
together with 1 kg of steam at
Ice and Steam
1) between 0oC and 50oC
100oC. What is the final
2) 50oC
temperature?
3) between 50oC and 100oC
LF = 80 cal/g, Lv = 540 cal/g
cwater = 1 cal/g oC
4) 100oC
5) greater than 100oC
ConcepTest 17.8
You put 1 kg of ice at 0oC
together with 1 kg of steam at
Ice and Steam
1) between 0oC and 50oC
100oC. What is the final
2) 50oC
temperature?
3) between 50oC and 100oC
LF = 80 cal/g, Lv = 540 cal/g
cwater = 1 cal/g oC
4) 100oC
5) greater than 100oC
How much heat is needed to melt the ice?
Q = m Lf = (1000g)  (80 cal/g) = 80,000 cal
How much heat is needed to raise the water temperature to 100oC?
Q = cwater m DT = (1 cal/g oC)(1000g)(100oC) = 100,000 cal
But if all of the steam turns into water, that would release 540,000 cal.
Thus, some steam is left over, and the whole mixture stays at 100oC.
Follow-up: How much more ice would you need?
ConcepTest 17.9
You’re in Hot Water!
Which will cause more severe burns
to your skin: 100 °C water or 100 °C
steam?
1) water
2) steam
3) both the same
4) it depends...
ConcepTest 17.9
You’re in Hot Water!
Which will cause more severe burns
to your skin: 100 °C water or 100 °C
steam?
1) water
2) steam
3) both the same
4) it depends...
While the water is indeed hot, it releases only 1 cal/g of heat as it
cools. The steam, however, first has to undergo a phase change
into water and that process releases 540 cal/g, which is a very
large amount of heat. That immense release of heat is what
makes steam burns so dangerous.
ConcepTest 17.10
You step out of a swimming
pool on a hot day, where the
air temperature is 90° F.
Where will you feel cooler, in
Phoenix (dry) or in
Philadelphia (humid)?
Spring Break
1) equally cool in both places
2) Philadelphia
3) Phoenix
ConcepTest 17.10
You step out of a swimming
pool on a hot day, where the
air temperature is 90° F.
Where will you feel cooler, in
Phoenix (dry) or in
Philadelphia (humid)?
Spring Break
1) equally cool in both places
2) Philadelphia
3) Phoenix
In Phoenix, where the air is dry, more of the water will
evaporate from your skin. This is a phase change,
where the water must absorb the heat of vaporization,
which it takes from your skin. That is why you feel
cool as the water evaporates.
ConcepTest 18.1
A free expansion occurs when a
valve is opened allowing a gas
to expand into a bigger
container. In such an expansion
the temperature of the gas will:
Free Expansion
1) increase
2) decrease
3) stay the same
ConcepTest 18.1
A free expansion occurs when a
valve is opened allowing a gas
to expand into a bigger
container. In such an expansion
the temperature of the gas will:
Free Expansion
1) increase
2) decrease
3) stay the same
In such a process:
W = 0 there is no object to move,
Q = 0 there is no heat exchange, therefore
DU = 0 by the First Law of Thermodynamics.
Thus, there is no change in the temperature.
Free expansion is an irreversible process --- the gas molecules have virtually no
chance of returning to the original state.
Free expansion is neither adiabatic nor isothermal
expansion, even though DT and Q are zero.
ConcepTest 18.2
In the closed thermodynamic
Work
1) positive
cycle shown in the P-V diagram,
2) zero
the work done by the gas is:
3) negative
P
V
ConcepTest 18.2
In the closed thermodynamic
Work
1) positive
cycle shown in the P-V diagram,
2) zero
the work done by the gas is:
3) negative
The gas expands at a higher pressure
and compresses at a lower pressure.
In general, clockwise = positive work;
P
counter-clockwise = negative work.
V
ConcepTest 18.3
The heat engine below is:
Heat Engine
1) a reversible (Carnot) heat engine
2) an irreversible heat engine
3) a hoax
4) none of the above
ConcepTest 18.3
The heat engine below is:
Heat Engine
1) a reversible (Carnot) heat engine
2) an irreversible heat engine
3) a hoax
4) none of the above
Carnot e = 1-TC/TH=1-270/600=0.55.
But by definition e = 1-QL/QH
=1 - 4000/8000=0.5, smaller
than Carnot e, thus irreversible.
Follow-up: What would you need to change to make it a Carnot engine?